JPH0613825A - Automatic gain control circuit - Google Patents

Abstract

PURPOSE:To attain a stable automatic gain control operation for the frequency of a sine wave of the input signal even though the frequency is approximate to the frequency of the amplitude fluctuation by accelerating the responsiveness of the automatic gain control. CONSTITUTION:An output signal S0 is inputted to a phase shifter 4 and a signal S0' having a phase delayed by 120 deg. is obtained. The signal S0' is inputted to a phase shifter 4' and a signal S0'' having a phase delayed by 120 deg. is obtained. Thus these signals S0, S0' and S0'' have the phase difference of 120 deg. respectively. Then the signals S0, S0' and S0'' are inputted to the detectors 3, 3' and 3'' respectively to undergo the half cycle detection. These detection outputs S3, S3' and S3'' are synthesized by a synthesizer 5, and an output S4 is obtained. The output S4 is equal to a perfect DC component and serves as the control signal of a variable attenuator 1. This signal S4 instantaneously has an answer to the signal S0.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an automatic gain control circuit (Auto
Gain Control Circuit; hereinafter referred to as AGC circuit).

[0002]

2. Description of the Related Art The structure of a conventional AGC circuit is shown in the block diagram of FIG. In FIG. 3, 1 is a variable attenuator, 2 is an amplifier, 3 is a detector, and 6 is an LPF (low-pass filter). In the AGC circuit of FIG. 3, the output signal S0
Is input to the detector 3 (for example, a diode or the like) to perform half-wave or double-wave detection. Here, since the detection output S3 has a ripple component, high-frequency components other than DC are
It is removed at F6 to obtain the DC component S4. Then, the variable attenuator 1 is controlled by the DC component S4 and its output S
i ′ is lowered and the output S0 is controlled to be constant by this closed loop.

[0003]

However, in the conventional AGC circuit as described above, when the amplitude (envelope) of the input signal Si changes with a sine wave of the frequency fi,
There is a problem that the followability with respect to amplitude fluctuation is poor.
Specifically, the LPF 6 of FIG. 3 has the gain and phase characteristics as shown in FIG. And in FIG. 4, θ is usually 90.
° or more. When the frequency of amplitude fluctuation is fN, when the phase delay of the LPF 6 at that frequency is almost "0", AG
Although the C circuit has sufficient followability, the LPF 6 has a frequency f
Since the signal i is removed, the upper limit frequency of the phase delay "0" of the LPF 6 is determined by the frequency fi. Therefore, when the frequency fN is close to the frequency fi, it is affected by the phase delay in the LPF 6. When this influence is exerted, the output signal S0 does not have a constant amplitude as shown by the broken line in FIG. 5, and phenomena such as insufficient amplitude and overshoot occur.

The present invention has been made in view of the above problems, and by accelerating the response of the automatic gain control, even if the frequency of the sine wave at the time of input and the frequency of the amplitude fluctuation are close, An object of the present invention is to provide an automatic gain control circuit capable of performing a stable automatic gain control operation of the frequency of a sine wave.

[0005]

To achieve the above object, the automatic gain control circuit of the present invention inputs an input signal whose amplitude component varies and controls the amplitude of the signal by a predetermined control signal. In the automatic gain control circuit that obtains the output signal, amplitude-detects the output signal, obtains the DC component, and sets it as the predetermined control signal, and controls so that the output signal has a constant amplitude. A phase difference output means for obtaining a phase difference output signal, a wave detecting means for amplitude-detecting each phase difference output signal to obtain a DC component, and a synthesis output signal as a control signal for synthesis And means.

[0006]

With the above structure, the automatic gain control circuit of the present invention is
A plurality of predetermined phase differences are given to the output signal by the phase difference output means to obtain each phase difference output signal and output to the detection means,
The detection means amplitude-detects each phase difference output signal to obtain a DC component. Then, the synthesizing means synthesizes the respective DC components and outputs a synthesized output signal as a control signal, and controls the amplitude of the input signal by using the outputted synthesized output signal as a control signal to obtain an output signal having a constant amplitude. In this case, the combined output signal, which is the control signal, can instantly respond to the change in the above-mentioned output signal.

[0007]

1 is a block diagram showing the configuration of an embodiment of an automatic gain circuit according to the present invention. In FIG. 1, 1 is a variable attenuator, 2 is an amplifier, 3, 3'and 3 "are detectors as detecting means, and 4 and 4'are 1 as phase difference outputting means.
The 20 ° phase shifter 5 is a combiner as a combining means.
FIG. 2 is a signal waveform diagram of the input (FIG. 2A) and the detection output (FIG. 2B) to the detector.

In FIG. 1, the output signal S0 is input to the phase shifter 4, and a signal S0 'having a 120 ° phase delay is obtained. Further, S0 'is input to the phase shifter 4', and a signal S0 'delayed by 120 ° in phase is obtained. As a result, the signals S0, S0 ', S
0 ″ is a signal having a phase difference of 120 ° as shown in FIG. 2A. Next, these signals S0, S0 ′,
When S0 "is input to the detectors 3, 3 ', 3" and half-cycle detection is performed, signals S0, S are generated as shown in FIG. 2B.
Half cycle components S3, S3 ', S3 "of 0', S0" are obtained. These half cycle components S3, S3 ', S
2 "is combined by the combiner 5, a combined output S4 shown by a thick line in FIG. 2B is obtained. This combined output S4 is a complete DC component that does not include the frequency component of fi which is the amplitude fluctuation component of the input signal Si. Become.

Further, as shown by the dotted line in FIG. 2A, the time t
When the amplitude increases from P1 to P1 'at S0' becomes P
2 to P2 ′, S0 ″ changes so as to increase from P3 to P3 ′. When this is detected, S3 ′ changes from P2 to P2 ′ and S3 ″ changes from P3 to P3, as shown by the dotted line in FIG. 5B. Change to '. Therefore, the output signal of the synthesizer 5 is as shown in FIG.
It changes from P4 shown by the thick line of B to P4 '. As described above, in the present invention, the control signal S4 of the variable attenuator 1 can instantly respond to the output signal S0.

As the phase shifter, an all-pass filter or a loss / compensated R / C or R / L fine / integrator can be used. Further, in the present embodiment, the detector has been described as performing half-cycle detection, but it is also possible to detect both waves. Further, although the phase shifter of 120 ° is used in the present embodiment, the phase shifter is not limited to this, and a further subdivided phase shifter may be used.

[0011]

As described above, according to the present invention, since it is not necessary to filter the detected signal with the LPF, the AGC is possible.
The response delay of control is significantly improved. Even if the frequency fi of the input signal and the fluctuation frequency fN of the envelope are close to each other, it is possible to perform a sufficiently stable AGC operation.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of an automatic gain control circuit of the present invention.

FIG. 2 is a signal waveform diagram of an input (partial view A) and a detection output (partial view B) to a detector.

FIG. 3 is a block diagram showing a configuration of an automatic gain control circuit according to a conventional method.

FIG. 4 is a frequency characteristic diagram of an LPF used in a conventional automatic gain control circuit.

FIG. 5 is a response characteristic diagram of a conventional automatic gain control circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Variable attenuator 2 Amplifier 3,3 ', 3 "Detector (detection means) 4,4' Phase shifter (phase difference output means) 5 Combiner (combining means)

Claims (1)

[Claims] 1. Inputting an input signal whose amplitude component varies,
The amplitude of the signal is controlled by a predetermined control signal to obtain an output signal, and the output signal is amplitude-detected to obtain a direct current component to be the predetermined control signal, and the output signal is controlled to have a constant amplitude. In the automatic gain control circuit, a phase difference output means for giving a plurality of predetermined phase differences to the output signal to obtain a phase difference output signal, and a detection means for detecting the amplitude of each phase difference output signal to obtain a DC component respectively. And a synthesizing means for synthesizing the respective DC components to obtain a synthetic output signal as a control signal.